To limit these risks of collision there are known solutions, which generally employ means that involve the intervention of human operators.
Thus, as far as the self-propelled vehicles are concerned, these not being towed by the ship, one known solution is to provide mooring means on the hull of the vehicle, for example securing rings, these securing means being arranged in such a way that the vehicle can be lifted while maintaining a horizontal position. Launch and recovery can then, for example, be performed using a winch mounted on a mobile gantry positioned at the rear of the ship, or even a crane, the gantry or the crane allowing the lifting winch to be positioned over the recovery zone. As a result, launch and lift are performed vertically, thus limiting the possibilities of collision with the ship during lowering or raising. As an alternative, the vehicle can be lifted by placing it in a gondola-like device which itself comprises suitable fixing points.
This type of solution can be applied, notably autonomously, to vehicles towed from the middle but is not, however, readily applicable to the case of vehicles that are towed from the front because, for obvious reasons of efficiency, it is desirable for it to be possible for the vehicle to be towed and handled using the one same cable. Handling using means such as those described hereinabove using a single cable would prove tricky because it entails the vehicle passing from the vertical position to the horizontal position during launch and vice versa during recovery. This handling further requires additional operations the purpose of which, once the vehicle has been lifted and positioned over the deck of the ship, is to lay the vehicle down flat on the deck of the ship or, more generally, on a storage area. These operations themselves generally require the intervention of human operators, which intervention is made trickier and more hazardous when the sea is rough.
As a result, as far as vehicles towed from the front are concerned, the solution generally preferred is to use a handling cable secured temporarily above the centre of gravity of the vehicle.
Another solution that is also used is handling based on the installation of means comprising an inclined ramp along which the vehicle slides in order to reach the surface of the water or leave the water and return to the ship. The ramp is generally configured so that it guides the vehicle in a straight path, thus avoiding the vehicle having to follow a lateral course. However, such a ramp is generally ill suited to use in heavy seas, because lateral movements of the vehicle could then damage that vehicle.
The use of such means advantageously allows the vehicle to be launched and deployed at the rear of the ship in a simple way by letting the towing cable out and, conversely, allows the vehicle to be returned on board the ship simply by winding the cable in, onto the drum of a winch for example. The launch and recovery of the vehicle can therefore moreover be performed while the ship is under way, which means that the vehicle, towed by the ship, naturally positions itself along the line of forward travel of the ship.
Nonetheless, the use of such means involves a critical phase which occurs between the moment the vehicle comes into contact with the ramp and the time it is fully in position thereon. Specifically, the transition of the vehicle from the surface of the water to the ramp involves the nose of the vehicle coming into contact with the ramp, and this contact, notably when the sea is rough, can be fairly violent and cause damage to the vehicle but also prevent the vehicle from being brought up.
In order to alleviate these difficulties of initial contact, various solutions have been developed, which solutions are generally best suited to one given type of vehicle. These known solutions generally involve reinforcing the structure of the vehicle, mainly the nose, so that it is able to withstand the knocks resulting from its coming into contact with the end of the ramp. It also involves the use of means for minimizing these impacts, particularly by configuring the ramp in such a way that its end lies beneath the surface of the water so that the vehicle floating on the surface comes into contact with the inclined surface of the ramp rather than with the end thereof. Such solutions nonetheless prove to be insufficient in rough seas, the slamming effect of the waves then being heightened by the movement of the ship.